Add Vector Search section

[andreibondarev]

I want to contribute to this list and help the maintainers, so:

• [x] I've accepted the terms of the CC0 License;
• [x] I've added the topic rubyml to the contributed repository if appropriate.

[andreibondarev]

@arbox Whenever you get a chance to glance this over :)

[arbox]

Thank you for your contribution :) Please see my comments attached.

[arbox]

Thank you!